The present invention relates to a laser device, and particularly relates to a laser device having an optical element for shaping a beam form of laser light into a desired form.
Conventionally, in a narrow band excimer laser device and fluorine laser device, a slit for shaping a sectional form of laser light into a predetermined form is known, and it is disclosed, for example, in Japanese Patent No. 2531788. FIG. 13 shows a configuration of an excimer laser device according to the prior art. It should be noted that FIG. 13 is made by being reversed horizontally relative to the drawing made in the aforementioned Patent. In FIG. 13, the excimer laser device 1 is seen from above, and in the explanation hereinafter, an up and down direction of the paper surface of FIG. 13 is called a lateral direction, and a direction vertical to the paper surface is called a vertical direction.
In FIG. 13, an excimer laser device 1 includes a laser chamber 2 containing laser gas being a laser medium at a predetermined pressure ratio, and inside the laser chamber 2, discharge electrodes 5 and 5 are placed to oppose to each other in the aforementioned vertical direction. High voltage is applied across the aforementioned discharge electrodes 5 and 5 from a high voltage power supply not illustrated to initiate discharge, and thereby the laser medium is excited in a discharge area 18 to oscillate laser light 11.
The laser light 11 excited in the laser chamber 2 is outputted from a rear window 9 toward the rear (the left side in FIG. 13), and its bandwidth is narrowed by a grating 23 so that a spectrum width of the laser light 11 become narrow. The laser light 11 with its bandwidth being narrowed enters the laser chamber 2 again from the rear window 9, and it outputted from the excimer laser device 1 through a front window 7 and a front mirror 38 to become a light source for processing of a processing unit such as a stepper or the like not illustrated.
In this situation, partial reflection coating for partially reflecting part of the laser light 11 at a predetermined ratio and transmitting and outputting the rest of the laser light 11 is applied on an entire surface of the front mirror 38 to the side of the laser chamber 2, and defines a partial reflecting element 26. The laser light 11 which is partially reflected by the front mirror 38 returns to the inside of the laser chamber 2, and is amplified again by discharge in the discharge area 18.
In front of and behind the laser chamber 2, placed are a front slit 16 and a rear slit 17 (described as xe2x80x9caperturexe2x80x9d in the aforementioned Japanese Patent No. 2531788) having a rectangular front opening 16A and rear opening 17A respectively. In the above prior art, the front slit 16 and the rear slit 17 correspond to optical elements for shaping the beam form of the laser light 11 into a desired form.
In the excimer laser device 1, part of the laser light 11 is cut by the aforementioned slits 16 and 17, and the sectional form of the laser light 11 is shaped into the form of the openings 16A and 17A so that the sectional form of the laser light 11 corresponds to a form required by a processing unit. Hereinafter, the sectional form of the laser light 11 is called a beam form.
The rear slit 17 shapes the beam form of the laser light 11 traveling rearward, thereby preventing disturbance of the wave surface caused by the laser light 11 hitting an end portion of the grating 23.
However, the aforementioned prior art has the disadvantage described below.
FIG. 14 shows a view taken along the 14xe2x80x9414 line in FIG. 13. It should be noted that the aforementioned lateral direction is represented as the left and right direction in FIG. 14. The illustration of the front window 7 is omitted. FIG. 15 shows a detailed configuration of the area near the front and the rear windows 7 and 9 of the excimer laser device 1.
As shown in FIG. 14, both the front opening 16A and the rear opening 17A according to the prior art are narrower than the discharge area 18 in which the laser medium is excited. As a result, even if the shape of the discharge area 18 is varied as a result of consumption of the discharge electrodes 5 and 5, the laser light 11 passing through the openings 16A and 17A can obtain a stable beam form.
However, as a result that the openings 16A and 17A are made narrower than the discharge area 18, as shown in FIG. 15, surplus laser light 11A, which is oscillated at the outer peripheral side of the discharge area 18 than the openings 16A and 17A, is cut by the slits 16 and 17. Thus, out of the discharge energy inputted into the discharge area 18, a part of it becomes a loss such as heat or the like and is not taken out as the laser light 11, which causes the disadvantage of reducing the efficiency of the excimer laser device 1.
Further, as shown in FIG. 15, the surplus laser light 11A is outputted to areas close to the openings 16A and 17A of the slits 16 and 17. Thus, the temperature in the areas close to the openings 16A and 17A of the slits 16 and 17 rise and thereby refractive index of the gas inside the openings 16A and 17A is varied, thus causing the disadvantage of the wave surface of the laser light 11 being disturbed. Furthermore, heat occurs in the areas close to the openings 16A and 17A of the slits 16 and 17 causes the slits 16 and 17 to have heat, which causes the disadvantage that impurities occurring there stain and damage the other optical components.
Further, in the rear slit 17, as shown in FIG. 15, the rear opening 17A is made smaller than the front opening 16A. Thereby, a part 11C of the laser light 11, which is partially reflected by the front mirror 38, passes through the front opening 16A, and returns to the discharge area 18, cannot pass through the rear opening 17A and is cut, thus further increasing the loss.
The present invention is made to eliminate the disadvantages of the above art, and its object is to provide a laser device capable of efficiently oscillating laser light and always obtaining a stable beam form.
In order to attain the above object, a first configuration of a laser device according to the present invention is in a laser device including an amplifying section in which a laser medium is amplified to oscillate laser light, and an optical element for separating part of the laser light oscillated in the amplifying section, and shaping a beam form of the laser light into a desired form to output the same,
the configuration in which the optical element has at least either one of a partial reflecting portion for partially reflecting the laser light or a non-reflective portion for transmitting the laser light at high transmissivity, each of which is provided on approximately a center portion, and a total reflecting portion which is provided outside a perimeter of said partial reflecting portion or said non-reflective portion, and which reflects the laser light at high reflectivity.
According to the above configuration, by allowing the laser light to pass through the partial reflecting portion or the non-reflective portion of the optical element, the beam form of the laser light to be outputted is shaped into the shape of the partial reflecting portion or the non-reflective portion. Recycle laser light separated by the optical element is reflected at the total reflecting portion with high reflectivity and returns to the amplifying section, where it contributes to laser oscillation. Accordingly, energy of the separated laser light is not lost, thus improving the energy efficiency of the laser device relative to the energy inputted for excitation.
A second configuration of the laser device according to the present invention is in a laser device including an amplifying section in which a laser medium is amplified to oscillate laser light,
the configuration including a front mirror having a partial reflecting portion which is provided on approximately a center portion and partially reflects the laser light, and a total reflecting portion which is provided outside a perimeter of the partial reflecting portion and reflects the laser light at high reflectivity,
in which the front mirror separates part of the laser light oscillated in the amplifying section, and shapes a beam form of the laser light into a desired form to output the same.
According to the above configuration, by outputting the laser beam from the partial reflecting portion provided on approximately the center of the front mirror, the beam form of the laser beam is shaped. Since the total reflecting portion is provided outside the perimeter of the partial reflecting portion, the laser light passing the portion outside the partial reflecting portion is reflected at the total reflecting portion with high reflectivity and returns to the amplifying section, where it contributes to the laser oscillation again. Accordingly, the energy loss of the laser light decreases, thus improving the energy efficiency of the laser device.
Further, in the present invention, since the front mirror also plays the role of the front slit placed between the front mirror and the laser chamber in the prior art, the front slit becomes unnecessary, thus reducing the number of components. In addition, since it is not necessary to place the front slit, the distance between the front mirror and the laser chamber is reduced, thus making the resonator length of the laser device shorter. Thereby, the laser device is reduced in size, and the loss in the resonator is reduced, thus increasing the power of the laser light.
A third configuration of the laser device according to the present invention is in a laser device including an amplifying section in which a laser medium is amplified to oscillate laser light,
the configuration including a prism having a non-reflective portion which is provided on approximately a center portion and transmits the laser light at high transmissivity, and a total reflecting portion which is provided outside a perimeter of the non-reflective portion and reflects the laser light at high reflectivity,
in which the prism separates part of the laser light oscillated in the amplifying section, and shapes a beam form of the laser light into a desired form to output the same.
According to the above configuration, by allowing the laser light to transmit the non-reflective portion of the prism, the beam form is shaped, and the laser light entering the total reflecting portion is separated and removed. Accordingly, in the present invention, the prism plays the role of xe2x80x9cthe rear slit placed between the laser chamber and the prismxe2x80x9d which is the conventionally ordinary configuration, thus making the rear slit unnecessary and reducing the number of components. As a result, the resonator length becomes smaller, the laser device is reduced in size and the loss in the resonator is reduced, thus increasing the power of the laser light. It should be noted that the configuration further including the front mirror in the aforementioned second configuration may be suitable. According to this configuration, the same operational effects as in the aforementioned second configuration is added.
A fourth configuration of the laser device according to the present invention is in a laser device including
an amplifying section in which a laser medium is amplified to oscillate laser beam,
a front slit and a rear slit which are provided to sandwich the amplifying section between them, and which separate part of oscillated laser light from the laser light and shape a beam form into a desired form to output the same, and
a front mirror for partially transmitting the laser light oscillated in the amplifying section to output the same,
the configuration in which the aforementioned front mirror has a low transmission portion with low transmissivity of the laser light, formed on approximately a center portion, and a high transmission portion with high transmissivity of the laser light, formed outside a perimeter of the low transmission portion.
According to the above configuration, of the laser light passing through an opening of the front slit, components which are conventionally partially reflected at the front mirror and cut by the rear slit pass through the portion with high transmissivity in the outer peripheral portion of the front mirror to be outputted outside. Accordingly, the components cut by the rear slit decrease, thus reducing the energy loss of the laser light, and improving the energy efficiency of the laser device.